With realization of miniaturization and high performance of a portable terminal, a wearable computer that can be attached to a human body has drawn attention. As information communication between such wearable computers, there has heretofore been proposed a method of connecting and attaching an electric field communication transceiver to a computer, and transmitting an electric field induced by this electric field communication transceiver through a human body as an electric field transmission medium to transmit/receive information.
FIG. 1 shows an electric field communication system according to a conventional technology.
A transmitter 201 in a portable terminal 200 modulates and outputs, based on a carrier wave having a predetermined frequency f, information (data) to be transmitted that is output from a small computer 206. The transmitter 201 is distant from an earth ground 209, and a stray capacitance Cg 207 is produced between a circuit ground 205 and the earth ground 209. Further, a stray capacitance Cb 208 is produced between a human body 210 and the earth ground.
According to the conventional technology, a reactance section 203 is interposed between a transmission circuit (a modulation/output section 202) and a transmission/reception electrode 204, and a voltage signal applied to the human body 210 is increased based on a resonance phenomenon with the stray capacitance to realize electric field communication (e.g., see Japanese Patent Application Laid-open No. 2004-153708, United States Application Publication, Pub. No. US2004/009226A1 Pub. Date: May 13, 2004).
However, in an electric field communication system that induces an electric field in the human body 210 as a medium and detects the electric field from the human body 210 that is in contact with the transmission/reception electrode 104 to perform communication, an electric field signal emitted from another device 105 that is not in contact with a receiver (an installed type device 102) is also detected. FIG. 1 shows a schematic view of an electric field communication system exposed to a radiation signal (noise) 106 from the other device (a radiation source) 105. It is to be noted that the other device may be a transmitter included in another electric field communication system that is not intended to perform communication.
When the radiation signal 106 from the radiation source 105 is data that has the same frequency and is modulated in accordance with the same modulation mode as a signal from the transmitter 201, it is difficult for a receiver 103 and a computer 101 to determine whether the received data is data from the radiation source 105 or data from the receiver 201 on a reception side.